Although the invention has general applicability to any given system where the formation and deposition of scale and in particular calcium phosphate is a potential problem, the invention will be discussed in detail as it concerns boiler water systems.
As is well known and comprehensively described and discussed in the Betz Handbook of Industrial Water Conditioning, 6th Edition, 1968, Betz Laboratories, Inc., Trevose, Pennsylvania, pages 151-171, the formation of scale and sludge deposits on boiler heating surfaces is the most serious water problem encountered in steam generation. Although current industrial steam producing systems make use of sophisticated external treatments of the boiler feedwater, e.g., coagulation, filtration, softening of water prior to its feed into the boiler system, those operations are only moderately effective. In all cases, external treatment does not in itself provide adequate treatment since muds, sludge, clay, silts, iron oxides and hardness-imparting ions, e.g., calcium, magnesium, and carbonate ions, escape the treatment and eventually are introduced into the steam generating system.
The problems which result from their introduction into the steam generating system are apparent. Since the deposit forming materials are present, they have a tendency to accumulate upon concentration of the water and to settle at points in the system where there is low flow thus restricting water circulation. The baking of mud and/or sludge on tubes and sheets will result in overheating and failure, thereby requiring down time for repair or replacement of the structural parts. In addition, mud, sludge, and silts may become incorporated in scale deposits, adding to their volume and heat insulating effect.
Accordingly, internal treatments have been necessary to maintain the mud and silts in a suspended state. These internal treatments have been generally referred to in the industry as sludge conditioning agents.
In addition to the problems caused by mud, sludge, or silts, the industry has also had to contend with boiler scale. Although external treatment is utilized specifically in an attempt to remove calcium and magnesium from the feed water, scale formation due to residual hardness, e.g., calcium and magnesium salts, is normally experienced. Accordingly, internal treatment, i.e., treatment of the water fed to the system, is necessary to prevent, reduce and/or retard formation of the scale-imparting compounds and their deposition. The carbonates of magnesium and calcium are not the only problem compounds as regards scale. Waters having high contents of phosphate, sulfate and silicate ions, occurring naturally or added for other purposes, are also problematic since calcium and magnesium, and any iron or copper present can react with each and form the respective complex insoluble salts, depositing as boiler scale. The problem is compounded by the deposition of iron oxides and clay with the other scale salts. Iron oxides enter the systems by escaping the pretreatment procedures and/or are present due to corrosion of the metal parts in contact with the aqueous medium. As is obvious, the deposition of scale, which by the present definition includes iron oxide, on the structural parts of a steam generating system causes poorer circulation and lower heat transfer capacity, resulting in an overall loss in efficiency.
Although the foregoing is directed to boiler water systems, or more specifically steam generating systems, the same problems occur in pulp and paper mill systems, cooling water systems, desalination systems (calcium sulfate formation and deposition), scrubber systems and the like. The problems encountered in these operations sometimes are more severe since complete external water treatments are not commonly utilized. Any aqueous system having calcium and magnesium cations and the exemplified anions, in particular phosphate and silicate, will experience the formation and deposition of the scaling salts.
Because of the foregoing, the water treatment industry is constantly evaluating new processes, new products, new techniques in an effort to permit the various process water systems to operate more effectively for longer periods and at lower costs.
Many and different type materials have been used for internal treatment of water systems, and in particular as sludge conditioning agents. Of the vast number may be mentioned alginates, lignins, lignosulfonates, tannins, cellulosic materials, synthetic polymers such as polyacrylates and in particular polymethacrylates, U.S. Pat. Nos. 2,723,956; 3,188,289; 3,549,538 are merely representative of the type materials used and the functions thereof. U.S. Pat. Nos. 2,723,956 and 3,549,538 disclose boiler treatments utilizing maleic anhydride and non-sulfonated styrene copolymers wherein the mole ratio of anhydride to styrene has an excess of anhydride and is at least 1:1 and preferably 2:1.